The embodiments disclosed herein relate generally to the field of Rankine cycle systems and, more particularly, to systems and methods for cooling expander components.
Rankine cycle systems are used to convert heat into electrical power. Traditional Rankine cycle systems create the heat by combustion of coal, natural gas, or oil and use a steam based working fluid. Organic Rankine cycle systems use a higher molecular mass organic working fluid than is used with the more traditional steam Rankine cycle systems. ORC systems may be used for heat recovery from low temperature heat sources such as industrial waste heat, engine exhaust, geothermal heat, photovoltaic systems, or the like. The recovered low temperature heat may be used to generate electricity, for example. Typically a closed loop system is used wherein the working fluid is pumped through an evaporator where the working fluid is evaporated, is pumped through at least one expander where energy is extracted, is pumped through a condenser where the working fluid is re-condensed, and is then pumped back into the evaporator.
In an ideal ORC, the expansion is isentropic, whereas the evaporation and condensation processes are isobaric. As a practical matter, during expansion, only a portion of the energy recoverable from the enthalpy difference is transformed into useful work. Increasing the temperature at the inlet of an expander increases the efficiency of the ORC system. Increasing the inlet temperature, however, also increases the temperature of the expander components. Some of the expander components may not be able to withstand the temperature of the thermodynamic optimum for ORC system efficiency.
It would be desirable to have a system and method that improves efficiency and power output of an ORC system.